The present invention relates to the recording and reproduction of binary data in disk storage systems for digital computers, particularly to a sampled amplitude read channel employing a post processor with a boundary error compensator which compensates for error events occurring at the boundaries of split-fields within a data sector recorded on a disk storage medium.
Post processors in sampled amplitude read channels for disk storage systems provide a significant increase in the effective signal-to-noise ratio (SNR) and thereby provide a significant increase in the linear density and overall storage capacity of disk drives. Sampled amplitude read channels typically employ a trellis sequence detector, such as a Viterbi sequence detector, for detecting a preliminary sequence from synchronous samples of the read signal. The accuracy of the preliminary sequence depends on the magnitude and character of the noise in the read signal; errors are typically due to a particular noise sequence resulting in a dominant error event associated with the trellis sequence detector. Post processors are employed to detect and correct these dominant error events, for example, by evaluating the signal noise to determine when a dominant error event was likely to have occurred. A remodulator remodulates the preliminary sequence into estimated sample values which are subtracted from the actual read signal sample values to generate a sequence of sample errors representing the noise in the read signal. A number of finite impulse response (FIR) filters process the sample errors in order to compute correlation values indicative of the dominant error events associated with the trellis sequence detector.
It is also known to employ an error detection code (EDC) for detecting when an error event occurred within a predetermined number of symbols in the preliminary sequence, and to correct the most likely error event (determined from the correlation values) that is consistent with the EDC error syndrome. For example, in the above-referenced U.S. Patent entitled xe2x80x9cSAMPLED AMPLITUDE READ CHANNEL EMPLOYING A REMOD/DEMOD SEQUENCE DETECTOR GUIDED BY AN ERROR SYNDROMExe2x80x9d a parity code EDC is employed to detect and correct certain dominant error events of a trellis sequence detector. A more sophisticated convolution code EDC capable of detecting and correcting additional dominant error events undetectable using a parity code EDC is disclosed in the above-referenced U.S. patent entitled xe2x80x9cAN ERROR DETECTION CONVOLUTION CODE AND POST PROCESSOR FOR CORRECTING DOMINANT ERROR EVENTS OF A TRELLIS SEQUENCE DETECTOR IN A SAMPLED AMPLITUDE READ CHANNEL FOR DISK STORAGE SYSTEMS.xe2x80x9d
When a data sector recorded on the disk comprises split-fields (e.g., when employing secondary sync marks or embedded servo sectors) a problem manifests in post processors employing an EDC in that error events occurring at the boundaries of the split-fields may be undetectable by the resulting EDC error syndrome. The EDC check symbols and corresponding error syndrome are typically generated only over the user data of a data sector and therefore any part of an error event extending over a split-field boundary will not be included in the EDC error syndrome. This problem arises both when an error event begins at the end of a user data segment and extends into an embedded field (e.g., into a secondary preamble or an embedded servo sector), and when an error event begins at the end of an embedded field and extends into a following user data segment.
There is, therefore, a need for a sampled amplitude read channel for disk storage systems employing a post processor responsive to an EDC and which compensate for error events occurring at the boundaries of split-fields within a data sector. In particular, there is a need to compensate for error events beginning at the end of a user data segment and extending into an embedded field (e.g., into a secondary preamble or an embedded servo sector), as well as error events beginning at the end of an embedded field and extending into a following user data segment.
The present invention may be regarded as a sampled amplitude read channel for reading a data sector recorded on a disk storage medium by detecting an estimated data sequence from a sequence of read signal sample values generated by sampling an analog read signal emanating from a read head positioned over the disk storage medium, the data sector comprising a user data segment and an embedded field comprising a known data segment. A sampling device samples the analog read signal to generate the read signal sample values and a trellis sequence detector detects a preliminary sequence from the read signal sample values. A post processor detects and corrects errors in the preliminary sequence using a syndrome generator responsive to the preliminary sequence representing the user data segment. The syndrome generator generates an error syndrome according to a predetermined error detection code. A boundary error compensator compensates for a boundary error event spanning the first user data segment and the known data segment. A guided error corrector, responsive to the error syndrome, corrects errors detected in the preliminary sequence.
The present invention may also be regarded as a method of reading a data sector recorded on a disk storage medium by detecting an estimated data sequence from a sequence of read signal sample values generated by sampling an analog read signal emanating from a read head positioned over the disk storage medium, the data sector comprising a user data segment and an embedded field comprising a known data segment. The analog read signal is sampled to generate the read signal sample values, and the read signal sample values are processed to detect a preliminary sequence. An error syndrome according to a predetermined error detection code is generated in response to the preliminary sequence representing the user data segment. A boundary error event spanning the user data segment and the known data segment is compensated. The error syndrome is used to correct errors detected in the preliminary sequence.